Radioactivity processing device



Oct. 27, 1959 0. K. NEVILLE ETAL 2,910,588

RADIOACTIVITY PROCESSING DEVICE Filed Feb. 8, 1957 3 Sheets-Sheet 1 Oct.27, 1959 0. K. NEVILLE ET AL RADIOACTIVITY PROCESSING DEVICE Filed Feb.8, 1957 3 Sheets-Sheet 2 Oct. 27, 1959 0. K. NEVILLE ETAL 2,910,588

RADIOACTIVITY PROCESSING DEVICE Filed Feb. 8, 1957 a Sheets-Sheet aFIELE RADIOACTIVITY PROCESSING DEVICE ()rear Kenton Neville, Elmhurst,and Benjamin F. Scott,

Chicago, Ill., assignors to Nuclear-(Ihicago Corporation, a corporationof Delaware Application February 8, 1957, Serial No. 638,980

14 Claims. (Cl. 250-44) This invention relates to radioactivityprocessing devices, and more specifically to devices employing radio-.activity to ionize air for the elimination of static elecplants andhospital operating rooms where there exists substantial hazard ofexplosion or other difliculties due to electrostatic charge, is toemploy a radioactive source whose emanations are directed against thebody whose charge is to be dissipated. Numerous objections to thistype'of device, however, exist. Such static elimination devices are ingeneral suitable only for the dissipation of charge over relativelysmall areas. Further, the rate of charge removal is seriously limitedby. the fact that the intensity of the radiation employed cannot be madevery high without constituting a hazard to personnel, unless elaborateprecautions are taken to prevent interposition of parts of the humanbody in the beam of radiation.

With these things in view, it has been proposed to remove the staticcharges by means of radioactivity indirectly, i.e., to blow a stream ofair over a source of radioactive emanations and thus to ionize the air,and then direct the ionized air against the charged body. See, forexample, the paper of Quinton given at Oxford in 1954 and published atpage 188, volume 2, fnadioisotope Conference, 1954, edited by J. E.Johnston (Academic Press Inc). Devices of this nature, however, have not"Ce ine into widespread use because of the large remaining hazardsjtopersonnel.

Although the ionized air itself has no substantial harmful effect shouldportionsof the human anatomy be interposed between thegenerator of theionized air and the surface upon which the ioni'zed air is directed,there nevertheless remains the substanti'al possibility of personsdeliberately or accidentally placing portions of' their bodies, such astheir hands, in

the direct beam of the radiation from the radioactive source, which isnormally'very intense in such application 's'. This hazard isparticularly acute because of the nature of the installations in whichsuch devices are designed to be used; In the vast majority of cases, thepersonnel in the industrial establishments, hospitals, etc'., in whichsuch static eliminators are required have no knowledge whatever ofradioactivity or of its dangers. The mere placing of warning signs,warning labels, and similar "safety paraphernalia has not been found tobe adequate to permit the use of such devices ordinary locations byuntrained personnel with any degree of safe ty.; The problem is evenmore acute because of the fact that the hazard from the radioactivity isunconnected with the operation or non-operation of the device. In thecase of most other types of hazardous devices, such as, for example,devices employing sources of high voltage,

the hazard exists only while the device is in operation. Inpreventinginjuries to personnel by such devices, it is .i'nerely necessary totrainv those persons who may have Contact with the device while it is inoperation. In the United States Patent O 2,910,588 Patented Oct. 27,1959 case of a device employing high intensity radioactivity, on theother hand, the hazard exists at all times, not only when the deviceisin operation, but when it is being shipped, when it is in a storeroom,or when it is in a junk-yard. It is thus obvious that the more trainingof personnel in the measures necessary to insure their personal safetyis inadequate to prevent the occurrence of accidents in the nature ofradiation exposure.

It is the principal object of the present invention to provide a staticeliminator device which is so safe that it is practical for use invirtually any type of installation, without the necessity of specialtraining of personnel. Furthermore, the safety features of the presentdevice are so designedthat the device is not only safe when used in themanner for which it is designed, but in addition will cause no damageeven under such extreme circumstances as might be encountered, if, forexample, it should be lost or stolen and tampered with by a personcompletely ignorant of its dangers, such as a child. In providing such astructure for a static eliminator, it is found that the safety featuresof the present device may well be incorporated in other radioactivityprocessing devices. Since the hazards incident to radioactivity asdiscussed above have constituted a severe limitation on the generalusage of radioactive materials in many other applications, theadaptation of the teachings of the present invention to a large varietyof radioactivity processing devices will readily be made.

The most serious aspect of a radiation hazard is the oumulation of thedamage done by the radiations. Momentary exposure to even a fairlystrong source, particularly in the case of ionizing radiations, such asalpha or beta particle emitters, will do little if any body damage.However, where a device incorporating a radioactive source is to bepermitted to appear in locations where it will be accessible to peoplecompletely ignorant of the nature of the device or its dangerouspotentialities, there exists the risk of prolonged exposure. As anexample, when an industrial establishment is determining whether toemploy a device incorporating a radioactive source in its plant, it mustconsider the possibility of tampering with the device by a completelyunauthorized person, who may,-for example, remove the source from thedevice and place it in a location wherein, unnoticed, it constantlyirradiates himself or one or more innocent persons who have no waywhatever of knowing of the existence of the source. This possibility hasconstituted a very serious deterrent to the use of equipment employingsuch sources in any type of location in which it is not practical totake elaborate precautions to prevent such of devices incorporating suchsources, it has been necessary to provide a variety of precautionsagainst such tampering, all of which add so tremendously to the cost ofpurchasing and using such equipment that devices employing radioactivityhave in general been shunned if any reasonable alternate has beenavailable.

In some radioactivity processing devices, it is possible to place thesource in a housing which serves as a shield and insert and removematerials to be irradiated through openings constructed and arranged toprevent the escape of radiations. in order to minimize the hazard ofhaving ignorant persons tampering with the device and exposing thesource, the shielding container may be securely locked, or evenpermanently sealed as by welding. However, reliance on a lock, no matterhow well designed, is uncertain at best. Permanent scaling is notsatisfactory,

since such permanent sealing makes it impossible to ever tion iscompletely secure against removal under all reasonable circumstances,the temptation is created to persons illicitly in possession of thedevice to saw through the shielding container (in ignorance of itsfunction) and to thus gain access to the interior, creating thehazardous condition described above.

The essence of the present invention lies in the provision of astructure wherein the source is contained in a shielded container withaccess openings designed to presource, and there are provided meansresponsive to breaching of the shield to open the container to diffusethe gas into the surrounding atmosphere. In the most advantageousembodiments of the invention, the radioactive gas employed is krypton85, which is known (see the paper of Arrol et al., at page 59 of thevolume above cited) to have the highly desirable characteristics ofbeing an intense source of beta rays of long half-life, but beingessentially harmless when released into the atmosphere, since it israpidly diffused and is immediately expelled by the human body ifinhaled.

For a more complete understanding of the teachings of the invention,reference is made to the embodiment illustrated in the appended drawing,in which:

Figure 1 is a top plan view of a radioactivity static eliminatorembodying the teachings of the invention;

Figure 2 is a transverse sectional view taken along the line 2--2 ofFigure 1;

Figure 3 is a longitudinal sectional view taken along the line 3-3 ofFigures 1 and 2; and

Figure 4 is a fragmentary view corresponding to a portion of Figure 3,but illustrating the manner in which a portion of the apparatus may bedisabled.

It will be seen that the shield or housing of the apparatus, of asuitable material such as 'altuninum, consists generally of a flat baseplate integral with a top portion 12 of arcuate cross-section and an endportion 14; at the other end is an end cover generally designated 16.The upper portion of the end cover 16 is provided with a tongue 18 ofarcuate cross-section and a peripheral shoulder 20 forming a stop forthe end of the top shield portion 12 into which the tongue 18 is thusclosely nested. A shorter tongue 22 on the bottom portion of the endcover 16 overlaps the end of the bottom plate 10, which abuts against ashoulder 24 on the cover. The cover is held in place by bolts 26, theheads of which are covered by a heavy metal strap 28. The strap 28 isseated in a groove 30 in the top shield 12, the groove 30 and the strap28 extending around the entire girth of the device except the base plate18. One end of the strap 28 is hinged at 32 to one side of the baseplate, and the opposite end of the strap 28 is locked to an ear 34,attached to the base plate, by a hasp 36 and a key-operated lock 38. Thestrap 28 is sufficiently resilient so that removal of the lock 38permits swinging away of the strap 28 from the cover to expose the headsof bolts 26. When the latter are removed, the cover may readily beremoved from the balance of the shield.

To each side of the upper surface of the base plate 10 are securedblocks 4% having diagonally cut sides 42 forming with the top surface ofthe base plate 10 an undercut keyway retaining a radioactive sourcecontainer 44. The source container 44 is generally rectangular ininternal shape and is formed from a block of suitable material such asstainless steel, with a radiation-perme- 4 able top closure. formed witha suitable diagonal pitch to slide in the keyway formed by the blocks40. One end of the container 44 abuts against the end portion 14 of theenclosure, and the opposite end of the container has an car 48 securedby a screw 50 to the base plate 10, thus locking the source containersecurely in place. The source container 44 may readily be removed uponremoval of the screw 50, after removal of the cover 16.

The upper wall of the source container 44 is a thin sheet of mica 52which is permeable to the radiations of the krypton contained within thesource container. The edges of the radiation-permeable wall or window 52are sealed to the body of the container 44 by fused glass 54. A plug 56of fused glass seals the filling aperture of the source container.

The end cover shield 16 is formed with an air inlet chamber 58 betweenthe outer end of the cover and a baffle plate 60 which has an airpassage slot 61 in the lower lower region thereof and is secured byscrews 62 to an internal shoulder 64 on the cover. The end of the coveris apertured in the upper region thereof at 66, and an air flow fitting68 is secured to the outer surface of the end cover and connected to theoutlet of an air blower 70. The latter, being of conventional design, isshown in the drawing merely in block form for purposes of simplicity.The opposite end of the housing is provided with an outlet dispersalnozzle 72 formed with an offset to prevent the exit of radiation. Boththe inlet and outlet air passages are of a size and shape to blockinsertion of human fingers into the interior of the housing.

Suspended from the inner surface of the top cover or shield 12 bybrackets 74 is a transversely extending pivot pin 76. Secured in centralposition on the pivot pin by hearing collars 78 is a knife having apointed and sharpened lower end at 82.

Wound about the pin 76 are helical springs 84 and 86 having their outerends secured to the brackets 74 and their inner ends hooked on the edgeof the knife 80 and urging the knife in the direction in which the point82 would penetrate the thin mica wall or window 52. However, the knife80 has a cam or stop portion 88 abutting against the tongue 18 of theend cover shield 16, thus maintaining the knife 80 in a withdrawnposition against the urging of the springs 84 and 86.

On the end of an extension 90 on the knife 80 is a ferromagnetic slug 92which is closely adjacent to a portion of the top of the housing whichhas an internally threaded well 94 filled by an externally threaded plug96 provided with a socket 98 which permits removal of the plug by meansof a suitable wrench.

As shown in Figure 4, there is employed as an auxiliary to the device astrong rod magnet 100 having the end thereof threaded in the same manneras the plug 96, so that the plug can be replaced by the magnet. When themagnet 100 is screwed into the well 94, the force of the magnet on theferromagnetic slug 92 draws the slug to the inner surface of the topshield portion 12, and thus latches the knife 80 against motion as longas the magnet 100 is in position.

The construction of the illustrated device having been described, thepurpose and mode of operation of the various features will be readilyunderstood. As indicated by arrows in the drawing, ambient air is drawnin by the blower 70 and blown into the aperture 66 and the air inletchamber 58. It enters the main body of the shielded chamber through theslot 61 and proceeds over the irradiation region adjacent to the windowor radiation-permeable Wall 52, the air thus ionized leaving the devicethrough the nozzle 72 to be dispersed over a surface on or adjacentto'which the device is placed. Both the offsetting of the inlet aperture66 and the slot 61 and the offset shape of the outlet nozzle 72 preventescape from the chambernot only of primary The outer surfaces of sides46 are radiations directly generated by the primary radiations.

The ionized air emitted by the nozzle 72 is harmless,

and produces no radiation effects.

It will thus be seen that the illustrated device is ,well

suited to accomplish the purpose of eliminating static electricity oversubstantial areas. The strength or. intensity ofthe radioactivity sourcemay be selected in accordance with the size of the device and theionization capacity whichit is designedto have. .In most applica tionsafew millicuries of krypton 85 may be successfully employed, but sourcesof much higher intensity may be used if. desired. Purity of the gas isnot critical, but where the gas isobtained as a fission product, it isof course necessary to remove contaminants which would impair. thesafety of the present device. Krypton 85 also producesa slight amount ofgamma radiation, but this creates no substantial hazard, being orders ofmagnitude smaller'than the beta radiation.

It isto be noted that the locking device comprising the strap28 whichoverlies the bolts 26, and its associated hinge and lock, is notdesigned to provide the maximum possible assurance against tamperingwith the device. On the contrary, perhaps the most important purpose ofthe locking device is to provide an obvious access point forunauthorized persons, who might otherwise create a serious radiation'hazard. The shield is constructed of a far thicker gauge material than isactually required for absorption of the beta radiations from the source.The rather insecure locking device, when'combined with the thickness ofthe shield, serves .toassure that ignorant persons attempting to gainaccess to the interior will do so by separation of the two portions ofthe enclosure. When access is gained in this manner, as the operation ofremoving the cover is commenced, the removal of the end of the tongue 18releases the knifei80, which thereupon, under the urging of the springs8 4 and $6, ruptures the window or wall 52, and thuspermits difiusion ofthe gas within the s me o a n ia q the. a mo e e The yp n 85 -r sd rsdompls alyharm sss br i h dispersion, v n

if 'kept within a sealed room of moderate size.

The auxiliary disabling means for the knife 80 consisting of theferromagnetic slug 92 and the magnet 100 is for use by authorizedpersonnel for the purpose of gainng access to the interior foroperations such as cleaning, it such should be necessary, or replacementof the 7 source. In addition, of course, the magnet 100 is employed todisable the knife when the device is being assembled Where the device isto be used in atype of installation where it is not desired that any ofthe personnel have access to the interior of the device, neither themagnet 100 nor instructions for opening are supplied to the user, themaintenance operations, if any are required, being performed solely bythe manufacturer or a suitable service agency, to whom the device isreturned for any such service that may be required. It is, of course,technicallypossible to disable the knife by insertion of any magnetsufliciently strong into the well 94, and thereupon to disassemble theshield without rupturing the window of the source. However, thelikelihood of this being done by any person who has not been instructedin the manner of opening the device or the nature of its internalconstruction is so small as to be completely negligible.

It will thus be seen that the illustrated static eliminator is highlysuitable for use in a location in which no special precautions are takenconcerning radiation hazards. It will be further seen that the essenceof the features of the construction of the device may be adapted to manytypes of devices for radioactivity processing of materials other thanair. Further, many variants of the construction shown will readily bedevised. Certain of the features can, if not necessary for particularapplications, be

omitted, and likewisejn some applications it will be desirable to addadditional features. Thus if access to the interiorwithout opening thenormally sealed source container is not required, no provision need bemadefor such access. Likewise the source container may be so shaped anddisposed that breaching of the shield in any fashion whatevernecessarily opens the source container. In another modification, theflat source container illustrated is mounted centrally, rather than atone side, of the irradiation region, and is provided withradiationpermeable windows on both sides. In a still furthermodification, the chamber through which the air flows is. enclosed in asurrounding chamber containing a non-radioactive compressed gas, =andrelease of the gas from the source container is accomplished in responseto a fall in pressure of the non-radioactive gas. V Obviously, theteachings of the invention will be adapted by persons skilled in the antto many embodiments far difierent in both appearance and details ofconstruction from the illustrated generator of ionized air. Accordingly,the scope? of the invention should not be deemed to be limited by theparticular embodiment thereof shown in the drawing, but shall bedetermined only by the appended claims.

What is claimed is t 1. A static electricity eliminator comprising atleast two wall portions forming a closed chamber having an air inletpassage and an air outlet passage each constructed and arranged to blockpassage of both primary and secondary beta particles from the chamber,an air blower operatively connected to one of said passages, a normallysealed container of krypton having a wall permeable to beta particleswithin the chamber, mechanism normally responsive to the motion or" oneof the wall portions with respect to the other of the wall portions toopen the container to diffuse the krypton 85, and means operable fromthe exterior of thechamberto disable the mechanism and thus to enableopening of the chamber while retaining the krypton 85 in the container..f 12. An ionized air generator comprising a closed chamb'er the openingof the chamber to disable the container I opening means.

3. A radioactivity processing device comprising a. chamber adapted toreceive a substance to be irradiated with beta particles, an accessopening to the chamber, a closure member, means for securing the closuremember over the access opening, a normally sealed container of krypton85 having a wall permeable to beta rays within the chamber, and meansresponsive to removal of the closure member to open the container topermitthe escape of the krypton 85.

4. A radioactivity processing device comprising 21 normally sealedcontainer filled with a radioactive gas and having a wall permeable tothe radioactive emanations from said gas, a shield substantiallysurrounding said wall and forming a chamber adjacent to said wall im- 6.A radioactivity processing device comprising a normally sealed containerfilled with a radioactive gas and having a wall permeable to theradioactive emanation from the gas, a shield impermeable to suchemanations surrounding said wall and forming an irradiation chamberadjacent to said wall, an access passage through said shield of a shapeand size to pass a substance to be irradiated but to block passagethrough the shield of any portion of the human anatomy, and meansresponsive to breaching of the shield to open the container to diffusethe gas into the surrounding atmosphere.

7. A static electricity eliminator comprising at least two wall portionsforming a closed chamber having an air inlet passage and an air outletpassage each constructed and arranged to block passage of both primaryand secondary ionizing particles from the chamber, an air bloweroperatively connected to one of said passages, a normally sealedcontainer of a gas emitting ionizing particles having a Wall permeableto such particles within the chamber, mechanism normally responsive tothe motion of one of the wall portions with respect to the other of thewall portions to open the container to diffuse the gas, and meansoperable from the exterior of thechamber to disable the mechanism andthus to enable opening of the chamber while retaining the gas in thecontainer.

8. A static electricity eliminator comprising at least two wall portionsforming a closed chamber having an air inlet passage and an air outletpassage each constructed and arranged to block passage of both primaryand secondary ionizing particles from the chamber, an air bloweroperatively connected to one of said passages, a normally sealedcontainer of a gas emitting ionizing particles having a wall permeableto such particles within the chamber, and mechanism responsive to themotion of one of the wall portions with respect to the other of the wallportions to open the container to diffuse the gas.

9. The device of claim 3 having externally operable means to disable thecontainer-opening means.

10. A safety-shielded radioactive source assembly comprising a normallysealed container filled with a radioactive gas, a shield enclosuresubstantially surrounding the container, means coupled to the containerand responsive to opening of the shield enclosure to open the containerto difiuse the gas into the surrounding atmosphere, and

eirternally operable me'ans independent of the opening of the shield todisable the container-opening means.

11. A safety-shielded radioactive source assembly comprising a normallysealed container filled with krypton 85, a shield enclosuresubstantially surrounding the container, means coupled to the containerand responsive to opening of the shield enclosure to open the containerto difiuse the krypton into the surrounding atmosphere, and externallyoperable means independent of the opening of the shield to disable thecontainer-opening means.

12. 'A radioactivity source adapted to be dissipated upon occurrence ofan unsafe condition comprising a container filled with krypton 85, atleast a portion of the container being permeable to beta rays, meansadjacent to thecontainer for opening the container to release thekrypton 85,and mechanism responsive to occurrence of the unsafecondition to actuate the opening means.

13. A radioactivity source adapted to be dissipated upon occurrence ofan unsafe condition comprising a container filled with a radioactivegas, at least a portion of the container being permeable to emanationsfrom the gas,

adapted'to pass a substance to be exposed to radioactivity, a normallysealed container of radioactive gas permeable to the radiation from saidgas withinlthe chamber, the chamber being of a material shielding the.ex-

, terior from radiations, and means responsive to opening of the chamberto open the container to disperse the radioactive gas.

References Cited in the tile of this patent UNITED STATES PATENTS2,675,487 Schallert et al. Apr. .13, 1954 2,723,349 Rylsky ....1 NOV. 8,1955 2,755,391 Keyes July 17, 1956 Martin Mar. 12, 1957

1. A STATIC ELECTRICITY ELIMINATOR COMPRISING AT LEAST TWO WALL PORTIONSFORMING A CLOSED CHAMBER HAVING AN AIR INLET PASSAGE AND AN AIR OUTLETPASSAGE EACH CONSTRUCTED AND ARRANGED TO BLOCK PASSSAGE OF BOTH PRIMARYAND SECONDARY BETA PARTICLES FROM THE CHAMBER, AN AIR BLOWER OPERATIVELYCONNECTED TO ONE OF SAIDF PASSAGES, A NORMALLY SEALED CONTAINER OFKRYPTON 85 HAVING A WALL PERMEABLE TO BETA PARTICLES WITHIN THE CHAMBERMECHANISM NORMALLY RESPONSIVE TO THE MOTION OF ONE OF THE WALL PORTIONSWITH RESPECT TO THE OTHER OF THE WALL PORTIONS TO OPEN THE CONTAINER TODIFFUSE THE KRYPTON 85, AND MEANS OPERABLE FROM THE EXTERIOR OF THECHAMBER TO DISABLE THE MECHANISM AND THUS TO ENABLE OPENING OF THECHAMBER WHILE THE KRYPTON 85 IN THE CONTAINER.